The two component developer which is employed in imaging machines such as copiers, printers and the like utilizing electrophotographic system is generally composed of a mixture consisting of a negatively charged toner and a positively charged carrier against the polarity of the charge of the toner. And the carrier is employed so as to enable the toner with an appropriate amount of triboelectric charge having a negative polarity.
In recent years, imaging machines such as laser printers in which the electrophotographic system is employed have tended to miniaturization. In accordance with the trend, in addition to the miniaturization of the imaging machines themselves, in particular, developing devices including developing units have been also miniaturized. In the small-sized developing device, there is inevitably provided a small amount of a developer for developing electrostatic images.
On account of the fact above, in the aforementioned two component developer to be negatively charged, it is required that an appropriate amount of trioboelectric charge is applied to the toner, that is, the charge rising properties are improved during a short period between the receipt of the toner and the transport to a developing zone for developing electrostatic latent images.
In view of the foregoing, as means for improving the charge rising properties, for example, Japanese Patent Publication Open to Public Inspection No. 2-8860 and the like disclose technology in that a charge control agent to be charged positively is added to and contained in a resin coating layer in a resin coated carrier.
Known charge control agents to be positively charged include quaternary ammonium compounds disclosed in Japanese Patent Publication Open to Public Inspection Nos. 49-51951 and 52-10141 and alkylpyridinium compounds and alkylpicolium compounds (for example, nigrosine SO, nigrosine EX, etc.) disclosed in Japanese Patent Publication Open to Public Inspection Nos. 56-11461 and 54-158932.
Conventionally known charge control agents to be positively charged have been organic compounds having a large cohesive force and have been inferior in being dispersed to and mixed with a coating resin. On account of the fact, it has been impossible to disperse uniformly the charge control agent to be positively charged to the resin coating layer of the carrier and to enable the toner with an appropriate amount of the negative triboroeletric charge. As a result, there has been a provided a problem in that toner scattering and background deposits on images are caused due to the fact that the toner is not enabled with an appropriate amount of the negative triboroelectric charge.